Towards light-induced quantum spin liquidity in an organic Mott insulator

Quantum spin liquids (QSL) are systems exhibiting long-range entanglement and spin fractionalization, where magnetic order is prevented by frustrated interactions and quantum fluctuations. The potential applications in topologically-protected quantum computing are stimulating great interest in QSL, but solid state realizations of these states of matter are still elusive. Several materials are predicted to be proximate to a QSL state, but extra interactions often alter the correct balance of magnetic frustration. Here, we excite the candidate QSL material κ-(BEDT-TTF)₂Cu₂(CN)₃ with ultrashort mid-infrared light pulses with the aim to nudge it towards a QSL phase. This compound is a prototypical Mott-Hubbard system formed by dimers of BEDT-TTF molecules arranged in a triangular lattice, which at 6 K exhibits a transition to a valence bond state [1]. We tune the interdimer and intradimer Coulomb repulsion via coupling to molecular excitations and investigate the effects on the spin degrees of freedom by probing the continuum of fractionalized spinon excitations [2] with single-shot THz spectroscopy [3]. We observe a transient increase in the THz optical conductivity at low temperature which is suggestive of an enhanced spinon spectral weight. These results open the possibility of a photoinduced quantum spin liquid state in κ-(BEDT-TTF)₂Cu₂(CN)₃ with mid-infrared vibrational excitation and advance the pursuit of ultrafast control of long-range entanglement in driven quantum materials.



References:

[1] B. Miksch, et al., Science 372, 276 (2021).

[2] S. Elsässer, et al., Phys. Rev. B. 86, 155150 (2012).

[3] F.Y. Gao, et al., Opt. Lett. 47, 3479 (2022).